ASSESSING THE GENOTOXICITY OF HEAVY METALS AND ORGANIC POLLUTANTS IN BURRUNAN DOLPHINS

Our current research aims to assess the health of the dolphins, trace the level of bioaccumulation of toxicants through the food-web and investigate the diet source.

Pollutants within an ecosystem biomagnify up the food chain and accumulate within the tissues of top order predators such as marine mammals. As such, dolphins are some of the best indicators of the bioavailability of pollutants and thus can be used as indicators for the health of an ecosystem. We know there are resident populations of Burrunan dolphins in Victoria which live almost exclusively within Port Phillip Bay or Gippsland Lakes. The levels of toxicants that may have accumulated in these resident dolphins is a direct bioaccumulation of the toxicants in these ecosystems and can therefore give us an indication of the overall health of these waterways.

PCBs and PAHs as well as mercury have been suggested to be related to mass mortality and population decline of some cetacean species, as a result of impaired reproductive success and immune defence (Taddei et al., 2001). The Burrunan dolphin has been found to contain some of the highest recorded mercury levels among all cetaceans worldwide (Monk et al., 2014), with beach-cast deceased individuals recording levels three times higher than those in the live population (Monk et al., 2014). Newer technologies now exist to assess, in real-time, the genotoxicity and stress impacts of heavy metal and organic toxicants on the Burrunan dolphins. However, to date there has been no analysis taken on the health of the animals, and therefore we cannot draw conclusions of the high but sub-lethal concentrations. Additionally, there is a need for a comprehensive food web study in order to calculate the amount of heavy metals and organic pollutants the Burrunan dolphin is consuming and trace the route of accumulation.

Recent advances in research and technology have allowed for improved methods for collecting and analysing biological samples of live animals in a less invasive manner. Using remotely acquired biopsy samples, Comet Assays and MICA protein expression can be performed to assess genotoxicity and stress respectively from the aforementioned toxicants. Biopsy sampling protocols are in accordance with current animal ethics and scientific permit conditions. One biopsy sample collected from free-swimming dolphins will allow genetic analyses (using the skin portion of the sample) and diet and/or toxicological analyses (from the blubber/skin portion). This small but important sample from living populations, coupled with fin identification, uses a multi-disciplinary approach encompassing studies on population & conservation genetics, and assesses health of the Burrunan dolphins. All animals will be identified prior to a biopsy, and since the scientists at MMF are familiar with each marked individual, there will be no risk of the same animal being biopsied more than once.

Aims:

• Assess health of the Burrunan dolphins by investigating the genotoxicity of heavy metals and organic pollutants (using COMET assays), and stress from pollutants (via MICA protein expression) in Burrunan dolphins.

• Investigate the diet of the Burrunan dolphins, to establish the route of bioaccumulation of toxicants within the animals.

  
  

BioAccumulation of Mercury

Our toxicology research has also previously focussed on identifying the sources and bioaccumulation mechanisms of mercury in the aquatic coastal food webs of Australia.

This collaborative research project, led by the Institute of Applied Ecology (University of Canberra), will assess the pathways for mercury (Hg) that enter and can be transmitted through food chains in coastal marine settings in south-eastern Australia. Mercury is one of the greatest threats to coastal and marine populations in Australia and worldwide as it has the potential to both bioaccumulate and biomagnify at the top of food chains. Iconic marine mammals, Burrunan dolphin (Tursiops australis), endemic to Port Phillip Bay (PPB), Victoria, are especially at high risk of mercury (Hg) poisoning due to their longevity and high trophic position (Monk et al. 2013).

Coastal zones are usually characterized by catchments that are heavily industrialized, have high population density and receive high inputs of toxins such as Hg through agricultural and urban drainages in addition to atmospheric deposition. In addition, highly productive coastal zones create favourable conditions for Hg methylation by anaerobic bacteria and bioaccumulation in food webs. Therefore, there is a strong need to determine Hg bioaccumulation and biomagnification rates in coastal food webs in order to minimize risks to iconic marine mammals and human-health from Hg contamination of coastal ecosystems.

The project will involve the collection of sediment and biota samples (seagrass, benthic algae, phytoplankton, zooplankton, zoobenthos, and fish) from vegetated and unvegetated habitats in shallow waters of Port Phillip Bay that overlap with dolphins feeding habitats and historical hot spots of elevated Hg concentrations. Both sediment and biota samples will be analysed for total Hg and selenium, methyl Hg, carbon and nitrogen isotopes and other trace elements by cutting-edge spectroscopy-based techniques (Perkin Elmer SCIEX Elan DRC-e ICP-MS, High Pressure Liquid Chromatography coupled to ICP-MS and isotope ratio mass spectrometer).

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PUBLICATIONS

Monk, A., Charlton-Robb. K., Buddhadasa, S. Thompson, R.M. (2014) Comparison of Mercury Contamination in Live and Dead Dolphins from a Newly Described Species, Tursiops australis. PLoS ONE 9(8):e104887. https://doi.org/10.1371/journal.pone.0104887

Abstract:

Globally it is estimated that up to 37% of all marine mammals are at a risk of extinction, due in particular to human impacts, including coastal pollution. Dolphins are known to be at risk from anthropogenic contaminants due to their longevity and high trophic position. While it is known that beach-cast animals are often high in contaminants, it has not been possible to determine whether levels may also be high in live animals from the same populations. In this paper we quantitatively assess mercury contamination in the two main populations of a newly described dolphin species from south eastern Australia, Tursiops australis. This species appear to be limited to coastal waters in close proximity to a major urban centre, and as such is likely to be vulnerable to anthropogenic pollution. For the first time, we were able to compare blubber mercury concentrations from biopsy samples of live individuals and necropsies of beach-cast animals and show that beach-cast animals were highly contaminated with mercury, at almost three times the levels found in live animals. Levels in live animals were also high, and are attributable to chronic low dose exposure to mercury from the dolphin's diet. Measurable levels of mercury were found in a number of important prey fish species. This illustrates the potential for low dose toxins in the environment to pass through marine food webs and potentially contribute to marine mammal deaths. This study demonstrates the potential use of blubber from biopsy samples to make inferences about the health of dolphins exposed to mercury.

Presentations

Courts, R., Erbe, C., Robb, K., Parnum, I. (2020) Marine soundscapes and bioacoustics of Victoria’s threatened Burrunan dolphin (Tursiops australis). Oral presentation. Victorian Biodiversity Conference. Melbourne.